The present invention relates to installation and removal of return springs for expanding shoe brakes for vehicles. The invention particularly relates to the installation and removal of hooked end dual coil type return springs employed in heavy duty truck drum brakes having dual ribbed arcuate brake shoes. Truck brakes of the aforesaid type are typically actuated by rollers provided on the ends of the shoe ribs which are contacted by an S-shaped cam which is mounted on a shaft rotated by the force of compressed air acting against a piston connected to the shaft by a suitable crank arm. Rotation of the shaft and S-shaped cam acting against the rollers spreads the brake shoes outwardly to force the brake linings attached to the shoes to frictionally engage the interior surface of the wheel drum for providing the desired braking action. The brake shoes are typically interconnected by a dual coil spring having the opposite ends thereof hooked over a pin provided between the ribs of each shoe adjacent the end contacting the S-shaped cam. The spring is stretched at assembly to provide a restraining force on the shoes away from the drum and to maintain the rollers in the end of the shoes in contact with the S-shaped cam.
In manufacture and service replacement, it has been found difficult to assemble the return spring onto the brake shoes after installation on the truck axle assembly; and, it has been found extremely difficult to provide a convenient way of stretching the springs for removal for replacement of brake shoes in field service. The stiffness of the return springs combined with the minimum clearance around the various components of the brake assembly have heretofore required complicated fixtures and tools to install the spring and to provide for removal for field service.
Thus, it has been desired to provide a low cost and convenient way or means of installing and removing brake shoe return springs employed in heavy duty truck brakes.